For example, there is a switching power supply apparatus such as a DC-DC converter, which performs switching so as to convert a DC high voltage into an AC voltage, and then converts the AC voltage into a DC low voltage. A magnetic device such as a choke coil and a transformer is used in the switching power supply apparatus.
For example, Patent Documents 1 to 6 disclose a board in which a coil pattern constitutes a winding wire of a coil, and a magnetic device which includes the board.
In Patent Documents 1 to 5, a core formed of a magnetic substance passes through the board. The board is formed of an insulating substance and has a plurality of layers. The coil pattern is formed on each of the layers so as to be wound around the core. Coil patterns on the different layers are connected to each other by using a through hole and the like. The coil pattern or the through hole is formed of a conductor of copper and the like.
In Patent Document 6, the board is formed of a pair of insulating layers and a magnetic layer interposed between the pair of insulating layers. A coil pattern formed of a conductor is formed on the magnetic layer. The coil pattern is obtained by performing winding multiple times in a plate face direction or a thickness direction of the board.
If a current flows in the coil pattern, heat is generated from the coil pattern and thus the temperature of the board becomes greater. As heat-dissipating measures for the board, the coil pattern is formed on almost of the entire area of each of the layers in the board in Patent Document 1. A heat radiator is attached to an end portion of the board.
In Patent Document 3, a portion of the coil pattern on each of layers in the board is widened and a heat-dissipation pattern portion is provided. A downward board protrudes from an upward board and the heat-dissipation pattern portion is provided on a protrusion portion so as to cause the heat-dissipation pattern portion to directly come into contact with an outside air. A position of the heat-dissipation pattern portion (provided in each of the layers) in a face direction is different.
In Patent Document 6, a heat-transfer through conductor which passes through the magnetic layer and a downward insulating layer is provided on an inside of the coil pattern. A heat-dissipation conductor layer connected to the heat-transfer through conductor is provided on a lower surface of the board. The heat-transfer through conductor and the heat-dissipation conductor layer are not connected to the coil pattern.